The hormone best known for its role in inducing labor may influence our ability to bond with others, according to researchers at the University of California, San Francisco. In a preliminary study, the hormone oxytocin was shown to be associated with the ability to maintain healthy interpersonal relationships and healthy psychological boundaries with other people. The study appears in the July issue of Psychiatry.

"This is one of the first looks into the biological basis for human attachment and bonding," said Rebecca Turner, PhD, UCSF adjunct assistant professor of psychiatry and lead author of the study. "Our study indicates that oxytocin may be mediating emotional experiences in close relationships."

The study builds upon previous knowledge of the important role oxytocin plays in the reproductive life of mammals. The hormone facilitates nest building and pup retrieval in rats, acceptance of offspring in sheep, and the formation of adult pair-bonds in prairie voles. In humans, oxytocin stimulates milk ejection during lactation, uterine contraction during birth, and is released during sexual orgasm in both men and women.

Turner and her colleagues tested the idea that oxytocin is released in response to intense emotional states in addition to physical cues. Twenty-six non-lactating women between the ages of 23 and 35 were asked to recall and re-experience a past relationship event that caused them to feel a positive emotion, such as love or infatuation, and a negative emotion, such as loss or abandonment. Because massage done on rats had previously been shown to influence oxytocin levels, the participants also received a 15-minute Swedish massage of the neck and shoulders. Blood samples were taken before, during, and after each of the three events to measure baseline oxytocin levels in the bloodstream and any change.

The results, on average, were of borderline significance - relaxation massage caused oxytocin levels to rise slightly and recollection of a negative emotion caused oxytocin levels to fall slightly. Recollection of a positive emotion, on average, had no effect.

What surprised the researchers, however, was how differently each woman responded. Some participants showed substantial increases and decreases while others were largely unaffected.

"We decided to look at the interpersonal characteristics of individual women to see if there was a correlation with changes in their oxytocin levels," said Turner, who is also the director of Student Research at the California School of Professional Psychology, Alameda campus. "We found a significant difference between women who reported distress and anxiety in their relationships and women who were more secure in their relationships."

Different questionnaires, including the Inventory of Interpersonal Problems and the Adult Attachment Scale, were used to assess each woman's previous experiences with personal and close relationships. The results were significantly correlated with the recorded changes in bloodstream oxytocin levels.

"It seems that having this hormone "available" during positive experiences, and not being depleted of it during negative experiences, is associated with well-being in relationships," said Turner.

In addition, women who were currently involved in a committed relationship experienced greater oxytocin increases in response to positive emotions than single women. The researchers speculate that a close, regular relationship may influence the responsiveness of the hormone, said Turner.

These preliminary findings bring up some intriguing questions, said Teresa McGuinness, MD, PhD, UCSF clinical psychiatry faculty member and co-author of the paper. Because oxytocin is released in men and women during sexual orgasm, it may be involved in adult bonding, said Turner. There is also speculation that in addition to facilitating lactation and the birthing process, the hormone facilitates the emotional bond between mother and child.

"Evolutionarily speaking, it makes sense that during pregnancy and the postpartum, both a woman's body and her mind would be stimulated to nurture her child," said Turner.

Oxytocin may also play a role in the higher levels of depression and interpersonal stress seen in women, said Turner. According to most psychiatrists, women experience depression twice as often as men and tend to be more affected by relationship difficulties. Turner and her colleagues hope that their work on oxytocin will guide future research on the psychiatric conditions of men and women.

"Our results provide the groundwork for further studies looking at the way hormones may be affecting human attachment," said Turner. "We know that oxytocin is one of the hormones that can facilitate bonding in other animals, but this is the first step in exploring whether it plays a role in the emotional behavior of humans."

In addition to Turner and McGuinness, authors of the paper include Margaret Altemus, MD, assistant professor of psychiatry at Cornell University Medical College; Teresa Enos, PhD, a graduate of the California School of Professional Psychology; and Bruce Cooper, PhD, professor at the California School of Professional Psychology."

Oxytocincould the 'trust hormone' rebond our troubled world? Lack of trust is at the root of many of the world's problems, says American neuro-economist Paul Zak, who claims to have found the brain chemical responsible for empathy. But could oxytocin really help to solve social issues? To read the full article click on the heart of Paul Zak.

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